1. Field of the Invention
The present invention relates to a profile producing method and a profile producing apparatus for producing a profile representative of the association between color data representative of values of for example red (R), green (G) and blue (B), or color data representative of dot % of cyan (C), magenta (Y) and black (K), and colors on a color image associated with image data including the color data, in a device for mediating between image data including color data and a color image, such as a color scanner and a color printer.
2. Description of the Related Art
Hitherto, it is performed that image data is obtained through reading a recorded original image by a color scanner and the like, and an image is outputted by a color printer in accordance with the image data thus obtained, so that an image, which is very closely similar in a color to the original image, is obtained, and an image, which is very closely similar in a color to an image obtained by printing based on the image data obtained by the color scanner, is outputted by a color printer. To perform a color matching for providing matching of colors of two images, there is used a profile defining the association between color data representative of dot % of CMYK for example, of an output device such as a color printer, and colors outputted in accordance with the color data, so that an image represented by a desired color can be obtained by a conversion of the image data using the profile. Here, the conversion as to colors is noticed. Hereinafter, such a conversion is referred to as a color conversion.
To make up such a profile, a color chart, consisting of sets of color patches associated with a plurality of sorts of color data wherein with respect to four colors of CMYK for example, dot % is sequentially varied as 0%, 40%, 70%, 100%, is outputted by an output device such as a color printer, and the color patches of the color chart thus outputted are measured by a calorimeter to obtain XYZ values defined by XYZ color system or L*a*b* values defined by CIELAB, so that color data of CMYK are associated with the XYZ values (or the L* a*b* values). Hereinafter, it is defined that the XYZ are values defined by the XYZ color system, and the L*a*b* are values defined by the CIELAB.
Basically, the profile is produced in the manner as mentioned above. However, the number of color patches constituting the color chart is not so large number that the number of color patches corresponds to that of the profile on a basis of one-to-one. Accordingly, it is performed to increase the number of pairs of the association between CMYK data and XYZ data (or L*a*b* data) by the interpolation operation and the like in accordance with a color association definition (here, the finally completed one is referred to as a “profile”, and the non-completed one is referred to as a “color association definition”) defining the association between CMYK data and XYZ data (or L a b data), which are obtained by a colorimetry of the color chart in the manner as mentioned above, and finally a desired profile is produced.
In the event that it is intended to obtain an output image by a color printer in accordance with image data obtained by a color scanner, color data included in the image data is modified using the profile produced in the manner as mentioned above, but not using the image data obtained by the color scanner, so that a desired color of image is outputted in accordance with the modified color data.
By the way, according to the above-mentioned method of producing a profile, it happens that the produced profile may include noises destroying monotonicity of variations of XYZ data or L*a*b* data to variations of color data of any of C, M, Y, K owing to measurement errors by a calorimeter, and characteristics of a device of an object of the profile to be produced, for example, characteristics of a color printer outputting of the color chart (for example, in some characteristics of the color printer, even if a color patch based on the same color data is concerned, it happens that colors of color patches are mutually different between a case where the color patch is recorded on the center of a paper and a case where the color patch is recorded on the edge of the paper). In the event that the produced profile includes such a noise, when the color conversion is performed using the profile, a jump in color density and a fluctuation in a hue direction will occur on a portion of gradation wherein density of a color is continuously varied, in a color image outputted based on image data after the color conversion, and thus there is a possibility that it is difficult to output a color image having an image quality which is high in color. Further, in the event that an inversion profile, wherein CMYK data is determined from XYZ data (or L*a*b* data) in accordance with the produced profile, is determined by a computation, there is a possibility that noises included in the profile become a main cause of errors of the computation, so that it is difficult to exactly determine the inversion profile.